Quantum well structures composed of nitride compound semiconductors which especially comprise InGaN are frequently used as an active layer in LEDs or laser diodes which usually emit in the blue spectral range. Depending upon the composition of the semiconductor material, emission in the ultraviolet, green, yellow or red spectral ranges is also possible. Luminescence conversion by luminescent materials enables short-wave radiation to be converted into larger wavelengths. In this way it is possible to generate mixed-colored light, especially white light. LEDs based on nitride compound semiconductors are therefore of considerable importance for LED lighting systems.
It has been found that the efficiency of LEDs having an InGaN-based quantum well structure declines at high current densities (the so-called “droop effect”). This effect is described, for example, in E. Kioupakis et al., “Indirect Auger recombination as a cause of efficiency droop in nitride light-emitting diodes,” Applied Physics Letters 98, 161107 (2011). It is assumed that an Auger-like recombination is the dominant loss mechanism in InGaN-based LEDs. That loss mechanism already occurs at current densities appreciably below the customary operating current density and brings about a reduction in the efficiency of the LED. It is assumed that the high Auger-like loss is caused by phonon-assisted Auger recombinations. Such phonon-assisted Auger recombinations occur in particular in InGaN-based semiconductor material. The reason for this is a strong electron/phonon interaction (high Huang-Rhys factor).
J. Ristié et al., “On the mechanisms of spontaneous growth of III-nitride nanocolumns by plasma-assisted molecular beam epitaxy,” Journal of Crystal Growth 310 (2008), 4035-4045, describes production of GaN-nanostructures. Further, W. Bergbauer et al., “N-face GaN nanorods: Continuous-flux MOVPE growth and morphological properties,” Journal of Crystal Growth 315 (2011), 164-167, describes production of nanostructures composed of GaN. The content of those publications is incorporated herein by reference.
There is nonetheless a need to provide an optoelectronic device having an active layer that comprises a quantum well structure based on a nitride compound semiconductor material, wherein losses caused by phonon-assisted Auger recombinations are reduced. At the same time the optical and electronic properties of the quantum well structure should otherwise be affected as little as possible.